Enteropathogenic E. coli (EPEC), an important food-borne pathogen, causes infantile diarrhea resulting in[unreadable] significant morbidity and mortality. However, the mechanisms of EPEC-induced diarrhea remain unclear.[unreadable] Diarrhea results from either increased secretion, decreased absorption, or both. Earlier studies have failed to[unreadable] conclusively show an increase in host secretory response by EPEC infection. Our preliminary data utilizing[unreadable] Caco-2 cells, showed that EPEC infection significantly inhibited the activities of both the predominant Na+[unreadable] absorbing isoform NHE3, the CI-OH exchanger and butyrate uptake. An analysis of the EPEC effects on[unreadable] NHEs showed that NHE1 and NHE2 activities were rapidly increased while the activity of NHE3 was[unreadable] significantly decreased. We hypothesize that one of the potential mechanisms of EPEC-induced diarrhea[unreadable] involves a decrease in intestinal absorptive processes. Our proposed studies will explore the effects of[unreadable] EPEC infection on intestinal NHE activities both in in vitro and an in vivo model and elucidate the[unreadable] mechanisms(s) underlying the differential regulation of NHEs by EPEC. Our Specific Aims are designed to:[unreadable] 1. To dissect the effects of EPEC on NHE isoform activities and Na+ flux in model human small intestinal[unreadable] (Caco-2.bbe) and non-transformed colonic (NCM460) epithelia; 2. Define mechanisms of EPEC-induced[unreadable] modulation of NHE isoform activities by elucidating signaling pathways involved, the role of regulatory factors[unreadable] (NHERF1 and NHERF2), the role of the cytoskeletal protein ezrin, and NHE membrane trafficking; 3.[unreadable] Examine the effects of EPEC on Na+ transport in ileum and colon in murine model of EPEC infection and in[unreadable] NHE2 & 3 knockout mice by determining the expression and activities of NHEs, transepithelial Na+ fluxes,[unreadable] gut luminal fluid accumulation, and the role of EPEC virulence genes. The results of these studies will[unreadable] enhance our understanding of the mechanisms of regulation of human intestinal NHEs and their modulation[unreadable] by pathogenic organisms. Our findings may aid in the future development of improved therapeutic modalities[unreadable] for infectious diarrhea.